Diquat in Drinking Water: Complete Guide (2026)

What is Diquat and Why Does It Matter?

DIQUAT: A HERBICIDE IN YOUR WATER SUPPLY

What Is Diquat and How Does It Get Into Tap Water?

Diquat is a fast-acting herbicide used to control aquatic weeds and algae in lakes, ponds, and irrigation systems. Farmers also spray it on crops like potatoes, soybeans, and grains to dry them out before harvest. When diquat is applied near water sources or in areas with heavy rainfall, it seeps into groundwater and surface water that communities rely on for drinking water. Unlike some contaminants that break down quickly, diquat persists in water for weeks or months, making it a stubborn problem once it enters the supply.

The chemical works by damaging plant cell membranes, which is exactly why it's concerning in drinking water—it can damage human cells too. Because diquat is widely used in agriculture across the United States, it's not a localized problem. Our data shows it detected in 71 water systems nationwide, with one system exceeding safe levels by a significant margin.

Health Effects and Exposure Risks

At low exposure levels, diquat hasn't been extensively studied in humans, which is part of why it's a concern. Animal studies show that diquat damages the lungs, kidneys, and liver when consumed in high doses. The Environmental Working Group (EWG) estimates that chronic exposure to diquat increases the risk of kidney damage and potentially cancer, though the evidence is still developing.

The EPA's current drinking water limit for diquat is 20 ppb (parts per billion). However, our data reveals one water system recorded 18.0 ppb—dangerously close to that threshold. The average level across affected systems is much lower at 0.528 ppb, but even "low" levels of a potentially toxic chemical deserve attention, especially for children and pregnant women whose developing bodies are more vulnerable to chemical exposure.

The gap between EPA limits and EWG recommendations is telling. While the EPA sets its standards based on older science and economic factors, the EWG's health-based guideline is typically more conservative. This means the EPA's "safe" level may not actually protect your family from long-term health risks.

The Regulatory Picture: Why Limits Keep Changing

Diquat sits in a regulatory gray zone. The EPA classifies it as a "possible human carcinogen," yet the drinking water standard of 20 ppb has remained unchanged since 1994. That's nearly 30 years of science that the EPA hasn't fully incorporated into updated rules. Meanwhile, the EWG and other health organizations argue the limit should be lower based on newer toxicology data.

The EPA did issue a Notice of Intent to regulate diquat more strictly in recent years, but regulatory changes move slowly. This gap between what regulators allow and what health experts recommend is why many families choose to filter their water rather than wait for government action.

Geographic Hotspots: Why Florida, Texas, and California Lead

Our data shows diquat concentrated in five states: Florida (23 systems), Texas (15), California (9), Louisiana (8), and Kentucky (3). This pattern directly reflects agricultural and aquatic herbicide use. Florida's extensive aquaculture industry and lake management programs rely heavily on diquat. Texas and California's massive irrigation operations use it to control weeds in canals and ditches. Louisiana's agricultural region faces similar pressures.

These aren't random hotspots—they're regions where diquat is sprayed regularly. If your community is in or near an agricultural area, your water system is at higher risk.

Removing Diquat From Your Drinking Water

Diquat isn't removed by standard carbon filters or basic pitcher filters. You need either granular activated carbon (GAC) filtration or reverse osmosis systems. Reverse osmosis removes up to 99.9% of diquat and other herbicides, making it the most reliable option for families in affected areas. Many municipal systems in diquat hotspots have already installed GAC treatment, but if your water tests high, a home reverse osmosis system provides an extra layer of protection.

Testing your water is the first step. If diquat is present in your area, a reverse osmosis system under your sink or a whole-home filtration unit ensures your family drinks clean water.

Regulatory Standards for Diquat

Cities With the Highest Diquat Levels

States Most Affected by Diquat

Frequently Asked Questions

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